1. Field of the Invention
The invention relates to (polyalkyl methacrylate) plastisols (PAMA plastisols) with improved flow properties achieved by the inclusion of hydrophilic monomers.
2. Discussion of the Related Art
Plastisols, i.e. two-phase systems comprised of plastic or synthetic resin particles and a suitable plasticizer or a suitable plasticizer mixture, can theoretically be produced from a variety of plastics, but until now, the applications with the greatest technical importance remained limited to a few polymer systems. Copolymerizates of poly(vinyl chloride) and other vinyl unsaturated monomers are known and are broadly used. A disadvantage here is their content of chlorine, which can have a corrosive effect under some conditions. These plastisols are also known as PVC plastics, plastisols, organosols, or plastigels (see also Ullmann""s Encyclopedia of Industrial Chemistry, 5th edition, Vol. A21, pages 734-737, (1992); Becker-Braun, Kunststoff-Handbuch (Plastics Handbook), 2nd edition, Vol., 2/2, pages 1077-1090, C. Hanser (1986); H. F. Mark et al., ed., Encyclopedia of Polymer Science and Engineering, 2nd edition, supplemental volume, pages 568-643, Wiley-Interscience (1989); and Saechtling, Kunststoff Taschenbuch (Plastics Pocket Book), Carl Hanser Verlag, Munich, 26th edition (1995), pages 406 ff.).
Copolymerizates based on methyl methacrylate and butyl methacrylate, so-called PAMA plastisols, are used with great success for plastisols in the automotive sector. The plastisols are used as adhesive plastisols, sealant compounds, welding pastes, and underbody protection compounds, as well as floor coverings. But plastisols on an acrylate basis have also been available for practical use for quite some time (see DE 934 498; FR-A 2,291,248).
The latter named state of the art is based on the recognition that for the production of technically acceptable PAMA plastisols, coordination of the glass transition temperature, Tg, the particle size, and the composition of the polymer particles, on the one hand, and special plasticizers, on the other hand, are required.
U.S. Pat. No. 4,371,677 (Goodrich) describes a production process for a copolymerizate of PVC and acrylate, in which the acrylate is continuously added during polymerization. The viscosity of the plastisol paste which can be obtained from the PVC copolymerizate is reduced.
From the references JP 04059849, xe2x80x9cCrosslinking via a chelate bondxe2x80x9d by using an additional resin (JP 50105725: melamine resin; JP 63137832: functional PVC resin with low molecular weight), by using isocyanates (JP 07164576, JP 56016533, JP 50077471, JP 59033344) it is known to polymerize monomers containing hydroxyl groups with vinyl chloride. In this way, crosslinking of the plastisol is achieved. PVC-free plastisols with monomers containing hydroxyl groups are described in EP 557944, JP-OS 07/157622, GB 2278116, WO 9426813, EP 624606, DE 3900933 and JP 8182838.
The purpose of the inclusion of monomers containing hydroxyl groups is crosslinking of the cured plastisol by means of esterification, JP-OS 07/102147 describes the adjustment of a solubility parameter.
The present application is directed to developing a suitable copolymer powder for poly(alkyl methacrylate) (PAMA) plastisols that clearly reduces the viscosity of the PAMA plastisol, while improving also the shelf life of the pastes obtained.
Reducing the viscosity of a plastisol paste makes it possible to mix in more additives, such as pigments, fillers, and other processing aids, while maintaining a comparable polymer content of the plastisol paste, before the limit of processability of the finished plastisol is reached by the user.
The user is therefore enabled, by the composition according to the invention, to work with the plastisol paste more extensively and therefore longer than with a plastisol of the state of the art, before the increasing viscosity of the resulting finished plastisol mixture sets limits for the user in terms of application technology.
This behavior of the composition according to the invention is unexpected because the compounds containing hydroxyl groups that are state of the art act as crosslinking sites.
It was now found that the addition of hydrophilic compounds results in a surprising improvement of the paste rheology. A compound of general formula III is used as a hydrophilic compound: 
Applicants have accomplished the above task by using a copolymer with the following composition:
a) 0-90 wt.-% of an acrylic acid alkyl ester with at least 3 carbon atoms in the alkyl radical and/or a methacrylic acid alkyl ester with at least 2 carbon atoms in the alkyl radical and/or styrene,
and
10-99 wt.-% methyl acrylate or methyl methacrylate or ethyl acrylate or ethyl methacrylate
c) 1-20 wt.-% of a hydrophilic compound of formula III 
or 2-dimethylaminoethyl methacrylate,
d) 0.01-1 wt. % of a crosslinking agent or a mixture of crosslinking agents and
e) 0-20 wt.-% of other monomers that can be radically polymerized. For example, (meth)acrylic acid, N-vinyl imidazole, itaconic acid, maleic acid, fumaric acid, or xcex1-methyl styrene can be used as component e).
The amounts of components a)-e) add up to 100 wt. %.
The copolymer powder obtained is processed to produce a plastisol, using known methods.
Such crosslinkable monomers according to component d) contain several units that can be radically polymerized, in the same molecule, for example such as a (meth)acrylic acid ester of multivalent alcohols. Examples that can be mentioned are trimethylol propane tri(meth)acrylate, 1,4-butane diol dimethacrylate, 1,3-butane diol dimethacrylate, 1,6-hexane diol dimethacrylate, and allyl methacrylate.
Production
The production of the polymers according to the invention takes place according to known methods, such as aqueous emulsion polymerization at a solid content of from 30 to 60 wt.%, preferable from 40 to 50 wt. % and more preferably about 50 wt. %, where the term about means plus or minus 5 wt. %. The copolymers according to the invention can be produced both as single-stage polymerizates and as multi-stage products.
Multi-stage polymerization processes yield a core-shell structure of the resulting particles, where the shells can also occur in multiple form, so that the core can be surrounded by several shells, each with a different composition.
Having generally described this invention, a further understanding can be obtained by reference to certain specific examples which are provided herein for purposes of illustration only and are not intended to be limiting unless otherwise specified.
The following Examples are also recited in the priority document, German patent application 199 14 605.5, filed Mar. 30, 1999, which is incorporated herein by reference in its entirety.